1. Field of the Invention
The present invention relates to an apparatus, and more particularly, to an apparatus for developing a pixel-defining layer of an organic light emitting diode.
2. Description of the Prior Art
Currently, an organic light emitting diode (OLED) display with light weight, high contrast, fast response speed, low power consumption and high brightness becomes the focus of the innovative generation display. However, compared with other mature displays, since the OLED display panel is the latest without perfect technique available, there are many difficulties in commercialization and mass production.
The OLED panel comprises a plurality of ITO anode electrodes, a plurality of photoresist separating walls perpendicularly positioned on the anode electrodes, an organic electroluminescent layer positioned between two adjacent photoresist separating walls on the anode electrodes, and a plurality of cathodes positioned on the organic electroluminescent layer. The anode and the cathode sandwich and the organic electroluminescent layer form a luminescent pixel of the OLED panel. In addition, a pixel-defining layer is created between the anodes and the photoresist separating walls to define the pixel pattern and dimension of the anodes. Also, the pixel-defining layer can isolate the anode and the cathode that laterally diffuses from the photoresist separating wall to promote the luminescent performance of the OLED panel.
In general, the pixel-defining layer is made of photoresist or polyimide (PI) wherein the PI with thermal, mechanical and electric stability is able to enhance the luminescent stability and the lifetime of the OLED panel. The method of forming the pixel-defining layer comprises the steps of coating the PI or the PI precursor, pre-baking, exposure, post exposure baking, development and curing. In the prior art of the development employed in semiconductor process or photoelectric process, a silicon substrate placed on a spinner is rotated and then the developer and the cleaning solution are sprayed on the silicon substrate. Next, the silicon substrate is spun at a high speed to remove the cleaning solution. Nevertheless, the traditional spinner can not bear the weight of the panel and the centrifugal force at a high rotary speed as the display panel with heavier glass substrate is enlarged followed by technical advances. This leads to imperfect development, remaining developer and in uniform pattern those greatly reduce the quality and yield of the display panel. Though the display panel can be immersed in a developing bath trough and a cleaning trough respectively to solve the above-mentioned problems, it still needs operators to deliver the display panel between two steps which will prolong the period time of the developing process. It is unfavorable to the mass production, especially to the display panel with large size. Also, it is not easy to control the delivering delay or damage resulted from the operators. Therefore, the prior art of the apparatus neither precisely control the developing time, nor ensure the quality of the developing process.
As for the polyimide, the chemical property of the polyimide remains unstable and easily damaged by alkaline solution before performing the final steps of the curing at the temperature between 220xc2x0 C. and 350xc2x0 C. Hence, it is needed to precisely control the developing time to prevent the polyimide being over etched by the developer. As for the nonphotosensitive polyimide, the development comprises the development of a photoresist layer and the etching of the nonphotosensitive polyimide not covered by the photoresist layer. If the developing time can not be controlled precisely, the polyimide could be over etched by the TMAH developer to damage the pattern of the PI pixel-defining layer and even make the polyimide stripped.
It is therefore a primary objective of the present invention to provide an apparatus for developing a pixel-defining layer of an OLED panel, which continuously conveys the display panel to each unit, shortens the period time of the developing process and applies to a mass production of the display panel with varied size.
In a preferred embodiment, the present invention provides an apparatus for developing a pixel-defining layer of an OLED panel. The apparatus comprises a developing unit for providing a developer on the display panel to persist a predetermined developing time; a cleaning unit for spraying a cleaning solution to remove the developer remaining on the display panel; a drying unit for drying the cleaning solution remaining on the display panel; a conveying unit for conveying the display panel to each of the connected units; and a control unit for determining a conveying sequence and a conveying time of the conveying unit so as to precisely control a processing time of the display panel in each of the units connected with the conveying unit. The conveying unit continuously conveys the display panel to the developing unit, the cleaning unit and the drying unit in sequence to complete the developing process, so the apparatus can precisely control the predetermined developing time, the quality of pixel-defining layers and effectively reduce the period of the developing process and the labor cost.
Besides, the apparatus can establish a plurality of developing units connected with each other to selectively employ the developing units depending on the request of maintenance or the developing process. Furthermore, the apparatus can establish a first stage cleaning unit for spraying a recycled cleaning solution and elementarily remove the developer, and a second stage cleaning unit for spraying a fresh cleaning solution and completely remove the developer. The used cleaning solution in the second stage cleaning unit is recycled to be the recycled cleaning solution in the first stage cleaning unit.
It is an advantage of the present invention that the apparatus precisely controls the predetermined developing time and possesses many options of using the developing units depending on the need of maintenance and the developing process. Also, it protects environment and reduces production cost by recycling the used TMAH and cleaning solution. Furthermore, it improves the lifetime and the operation efficiency of the apparatus.
This and other objective of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.